Electric primary cell



June 9, 1953 w. F. HIGGINS Erm. 2,641,622

ELECTRIC PRIMARY CELL Filed April 25, 1952 F/GJ,

MWMM

.A ttorney Patented June 9, 1.953

ELECTRIC PRIMARY CELL William F. Higgins and Robert Geolrey WilkinA son, Clifton Junction, near -Manchester, England, assignors to Magnesium Elektron Limited, Clifton Junction, near Manchester, England Application April 25, 195,2,.Serial No. 284,264

. .In Great Britain April 27,A 1951 -8 Claims. (Cl. 13d-120) 'Thisinventionrelates to electric primary cells ofthe kind commonly. ,known as dry cells .having an Vanode usually in the form ofl an outer casing Which is consumed rby the action of the'electrolyte when the cell is-producing current.

the-construction Vof dry cells it is one practical requirement that the reaction between the vanode .material and the constituents of the electrolyte whichproduces vcurrent Vwhen the cell is in operation, should not take place, or should take placelto the smallest. possible degree, when the cell-is not in,y use. .This freedom from reaction when not required is the factor which results in what is known as a -good shelf life Whichimplies that when the cell is tested after a period of storage,V a largepercentage of-the original capacity can still be obtained.

v.ln dryy cells of the Le Clanche type as commonly providedthe Vanode is zinc and the electrolyte containsammonium chloride as the chief active electrolyte reagent.- `In such cells a good sheltlife has beenachieved usuallyby having regardY to the vpurity of the materials-usedv-andl bychoice ofV .suitable concentrations of the. ingredients. .In dry cells in which the anode may be made of magnesium.- magnesium base alloys, aluminium, --orv aluminiuml base alloys, the achievement of a good shelf life leaves much to be desired -andimethodssarestill being sought to achieve improvements in this respect.

We have made experiments which show that the principles of galvanic protection by sacrifcial anodes composed of. metals or alloys more electro-positive -(more anodic) than the metals or alloys of which the normal cell anodes are composed can be -applied successfully in such cases to-achievethe result desired. The electrochemical relationship between the various metals and alloys is governed chiefly by the nature of the electrolyte in which they are immersed and whatever the metal chosen to form the normal cell anode, and whatever the electrolyte in which that anode is intended to work, it is usually possible to choose another metal or alloy (which however will generally be different in each case) such that the latter is still more electro-positive (more anodic). If this is done and the normal anode and sacrificial anode are coupled together electrically then the cell anode becomes cathodic to the sacrificial anode and the reaction which would normally ensue during storage between the normal anode and the electrolyte will be transferred to the sacrificial anode, which will be corroded according to the usual electrochemical principles and the cell anode will be cathodically protected against corrosion.

It has previously been suggested to attach sacrificial anodes to fuel .tanks `having steelstuds, and to Water pipes orother structures buried in the earth or immersed in the sea. In such uses, the object is to prevent or minimise corrosive attack on the tank or other structure at all times. In the case of dryI` cells however, it is necessary that the zinc-casing or like anode `shall be readily attacked invthe'lnormalvway by the action of the electrolyte whenthe cell isconnected for producing current and it is only desired to prevent corrosive attack-on this normal anode during periods of storage. The use ofa vsacrificial anode in a dry cell in accordance with-therpresent invention provides Ythe krequired protection of thenormalanode during-storage without Ain terfering with the attack -onfthe normal anode when the cell is'producingcurrent and without impedingV or diminishing the-current or voltage during use. l

As examples lof the eiiect above described, We instance thefollowing: f

1. It is possibles to embed a small piece of magnesium lalloy inthe-electrolyte paste of a normal Le Clanchevcell and-to connect this to thezincoutercasing. When this is done the zinc becomes-cathodic to the magnesium alloy during the time the cell isy onopen circuit vand is protected thereby. When the circuitis closed the zinc is,still:anodic to lthe-carbon cathode of the cell and-its performance is Anot hindered by the presence of the magnesium attached to it.

`-,2. Where zinc/is used in .stronglyalkalineelectrolyte it is possi-ble to adjust the pH of the electrolyte sow-that aluminiumis {anodic to the Zinc. Inisuch` acase a small Ypiece of aluminium connected tothe zincanode willsuccessfully protect the -latterfduringfperiods .of open circuit.

3. Where magnesium alloys which contain small percentages of aluminium or of zinc or of both (such for example as alloys known as Elektron (registered trade-mark) A231) are used to form the anodes of dry cells, pure magnesium will be found to be anodic to these alloys in most electrolytes and may be used for the purpose proposed.

y 4. Where magnesium alloys or pure magnesium are used to form the anodes of dry cells, magnesium base alloys containing lithium, calcium or sodium can be used.

5. In certain special cells containing nonaqueous electrolytes still more electropositive metals may be used and in general the more electropositive metal is used as the sacrificial anode to protect a less electropositive one which forms the cell anode. Thus sodium or potassium in certain cases could be used to protect lithium and calcium and lithium and sodium, to protect magnesium.

The sacricial anode may conveniently be in the form of a small block or rod inserted in the electrolyte within the upper end of the outer metallic casing which is to be protected in firm contact therewith. The sacrificial anode may alternatively consist of a ring or tube fitting tightly within said casing or may consist of a piece of wire bent to a U-shape, semi-circular shape or the like and sprung tightly into the casing.

As a further alternative a blank from which the casing is to be formed by die pressing may consist of the casing metal to one side of which is attached the metal for the sacrificial anode so that when the easing is formed the sacrificial anode constitutes a lining over whole or part of the inner surface of the casing. In some cases such a lining may be provided by rolling, spraying or otherwise.

If desired a vent may be provided for escape of gases which may be generated Within the cell.

The cell may otherwise be constructed in the usual manner.

Certain constructional forms of the invention will now be described with reference to the accompanying diagrammatic drawings wherein:

Figure l is a vertical sectional View of a primary cell made in accordance with the invention; and

Figures 2 and 3 are similar Views showing a modied construction. l

A casing I constitutes a metal anode which is consumed during the normal use of the cell. A carbon rod II constitutes the cathode and is mainly disposed within the casing. The cell has a bituminous covering I2 through which the upper end of the carbon rod projects and a brass cap I3 covers the top of the rod. The covering I2 has an escape outlet I5 for gases. A dolly containing a depolariser surrounds the lower part of the carbon rod and an electrolyte paste I1 is iilled into the casing around the dolly. A rod or wire I8 is bent into annular or part annular shape and is sprung into the casing so as to have a good electrical contact therewith and is disposed within the electrolyte around the upper end of the dolly.

In the modification shown in Figure 2 a small 4 therewith and in the nished cell the lower end of the bar 22 is below the dolly while the upper ends are adjacent the top of the electrolyte.

We claim:

1. An electric dry cell having a consumable metal anode, a cathode, an electrolyte, and a sacrificial anode made of a metal or alloy more electropositive than the said metal anode, the sacrificial anode allowing the metal anode to be consumed during normal use of the cell but minimising the corrosion of the metal anode during periods when the cellis not in use.

2. An electric dry cell as claimed in claim l wherein the metal anode is zinc and the sacricial anode is magnesium or magnesium base alloy.

3. An electric dry cell as claimed in claim 1, comprising a zinc casing constituting the metal anode, a carbon rod located partly within the casing, a depolariser dolly surrounding the lower part of the carbon rod, an electrolyte surround-V ing the dolly, a covering substanceover the zinc casing through which the upper end of the carbon rod projects, and a piece of magnesium or magnesium alloy in the electrolyte constituting said sacrificial anode and contacting the casing.

4. A cell as claimed in claim 3 wherein the sacrificial anode is annular or part annular in shape and located around the upper end of the 7. A een es claimed in claim 1 wherein the metal anode is a magnesium base alloy and the rod or plate 20 constitutes the sacriflclal anode sacrificial anode is pure magnesium. y 8. A cell as claimed in claim '1 wherein the metal anode is pure magnesium and the sacrificial anodel is a magnesium base alloy containing at least one metal selected from the group consisting of lithium, calcium and sodium. l

WILLIAM F'. HIGGINS. ROBERT GEOFFREY WILKINSON.

References Cited in the le of this patent UNITED STATES PATENTS Name Number Date OTHER REFERENCES National Battery Co. Report On The Theo-Ay retical Power Output of Storage Batteries, 1947, page 5.

Heise May v3, 19:'12; 

1. AN ELECTRIC DRY CELL HAVING A CONSUMABLE METAL ANODE, A CATHODE, AN ELECTROLYTE, AND A SACRIFICIAL ANODE MADE OF A METAL OR ALLOY MORE ELECTROPOSITIVE THAN THE SAID METAL ANODE, THE SACRIFICIAL ANODE ALLOWING THE METAL ANODE TO BE CONSUMED DURING NORMAL USE OF THE CELL BUT MINIMISING THE CORROSION OF THE METAL ANODE DURING PERIODS WHEN THE CELL IS NOT IN USE. 